Light emitting diode with three-dimensional nano-structures

ABSTRACT

A light emitting diode including a substrate, a first semiconductor layer, an active layer, and a second semiconductor layer is provided. The first semiconductor layer includes a first surface and a second surface, and the first surface is connected to the substrate. The active layer and the second semiconductor layer are stacked on the second surface in that order, and a surface of the second semiconductor layer away from the active layer is configured as the light emitting surface. A first electrode electrically is connected with the first semiconductor layer. A second electrode is electrically connected with the second semiconductor layer. A number of three-dimensional nano-structures are located on the surface of the first surface of the first semiconductor layer and the light emitting surface, and a cross section of each of the three-dimensional nano-structures is M-shaped.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. §119 from China Patent Application No. 201110395473.2, filed on Dec. 3, 2011 in the China Intellectual Property Office, disclosure of which is incorporated herein by reference. This application is related to applications entitled, “LIGHT EMITTING DIODE”, filed May 23, 2012 Ser. No. 13/479,223; “LIGHT EMITTING DIODE”, filed May 23, 2012 Ser. No. 13/479,225; “METHOD FOR MAKING LIGHT EMITTING DIODE”, filed May 23, 2012 Ser. No. 13/479,229; “LIGHT EMITTING DIODE”, filed May 23, 2012 Ser. No. 13/479,230; “METHOD FOR MAKING LIGHT EMITTING DIODE”, filed May 23, 2012 Ser. No. 13/479,232; “LIGHT EMITTING DIODE”, filed May 23, 2012 Ser. No. 13/479,233; “METHOD FOR MAKING LIGHT EMITTING DIODE”, filed May 23, 2012 Ser. No. 13/479,234; “LIGHT EMITTING DIODE”, filed May 22, 2012 Ser. No. 13/477,273.

BACKGROUND

1. Technical Field

The present disclosure relates to a light emitting diode (LED).

2. Description of the Related Art

LEDs are semiconductors that convert electrical energy into light. Compared to conventional light sources, LEDs have higher energy conversion efficiency, higher radiance (i.e., they emit a larger quantity of light per unit area), longer lifetime, higher response speed, and better reliability. LEDs also generate less heat. Therefore, LED modules are widely used as light sources in optical imaging systems, such as displays, projectors, and so on.

A typical LED commonly includes an N-type semiconductor layer, a P-type semiconductor layer, an active layer, an N-type electrode, and a P-type electrode. The active layer is located between the N-type semiconductor layer and the P-type semiconductor layer. The P-type electrode is located on the P-type semiconductor layer. The N-type electrode is located on the N-type semiconductor layer. Typically, the P-type electrode is transparent. In operation, a positive voltage and a negative voltage are applied respectively to the P-type semiconductor layer and the N-type semiconductor layer. Thus, holes in the P-type semiconductor layer and photons in the N-type semiconductor layer can enter the active layer and combine with each other to emit visible light.

However, the extraction efficiency of LEDs is low because the contact area between the N-type semiconductor layer and the active layer is not large enough. Thus the electron-hole recombination density is low, and the photons in the LED are sparse, thereby degrading the extraction efficiency.

What is needed, therefore, is a light emitting diode which can overcome the above-described shortcomings.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

FIG. 1 shows a schematic view of one embodiment of an LED.

FIG. 2 is an isometric view of one embodiment of a three-dimensional nano-structures array in the LED of FIG. 1.

FIG. 3 shows a scanning electron microscope (SEM) image of the three-dimensional nano-structures array of FIG. 2.

FIG. 4 shows cross-sectional view along a line IV-IV of FIG. 2.

FIG. 5 shows a schematic view of the second semiconductor layer of FIG. 1.

FIG. 6 shows a schematic view of another embodiment of an LED.

FIG. 7 shows a schematic view of the active layer of FIG. 6.

FIG. 8 shows a schematic view of another embodiment of an LED.

FIG. 9 shows a schematic view of another embodiment of an LED.

DETAILED DESCRIPTION

The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one.

Referring to FIG. 1, an LED 10 includes a substrate 100, a first semiconductor layer 110, an active layer 120, a second semiconductor layer 130, a first electrode 112, and a second electrode 132. The first semiconductor layer 110 includes a first surface and the second surface opposite to the first surface. The substrate 100 contacts with the first surface of the first semiconductor layer 110. The active layer 120 and the second semiconductor layer 130 are stacked on the second surface of the first semiconductor layer 110, and in that order. The surface of the second semiconductor layer 130 away from the active layer 120 is configured as the light emitting surface of LED 10. The second surface of the first semiconductor layer 110 defines a plurality of three-dimensional nano-structures 113. The light emitting surface of the LED 10 defines a plurality of three-dimensional nano structures 133. The first electrode 112 is electrically connected with the first semiconductor layer 110, and the second electrode 132 is electrically connected with the second semiconductor layer 130.

The substrate 100 can be made of a transparent material and adapted to support the first semiconductor layer 110. A shape or a size of the substrate 100 is determined according to need. The substrate 100 includes an epitaxial growth surface 101 which is used to grow the first semiconductor layer 110. The epitaxial growth surface 101 is a clean and smooth surface. The substrate 100 can be a single-layer structure or a multi-layer structure. If the substrate 100 is a single-layer structure, the substrate 100 can be a single crystal structure having a crystal face used as the epitaxial growth surface 101. If the substrate 100 is a multi-layer structure, the substrate 100 should include at least one layer having the crystal face. The material of the substrate 100 can be GaAs, GaN, AN, Si, SOI, SiC, MgO, ZnO, LiGaO₂, LiAlO₂, or Al₂O₃. The first semiconductor layer 110 and the substrate 100 should have a small crystal lattice mismatch and a thermal expansion mismatch. The size, thickness, and shape of the substrate 100 can be selected according to need. In one embodiment, the substrate 100 is a sapphire substrate with a thickness of about 40 nm.

The first semiconductor layer 110 is formed on the epitaxial growth surface 101. The first semiconductor layer 110 is an N-type semiconductor or a P-type semiconductor. The material of the N-type semiconductor can include N-type gallium nitride, N-type gallium arsenide, or N-type copper phosphate. The material of the P-type semiconductor can include P-type gallium nitride, P-type gallium arsenide, or P-type copper phosphate. The N-type semiconductor is configured to provide photons, and the P-type semiconductor is configured to provide holes. The thickness of the first semiconductor layer 110 ranges from about 1 μm to about 5 μm. In one embodiment, the first semiconductor layer 110 is an N-type gallium nitride doped with Si. The first semiconductor layer 110 includes a first surface and a second surface opposite to the first surface. The first surface is contacted with the substrate 100. The second surface includes a first region and a second region based on their function. The first region is used to locate the active layer 120 and the second semiconductor layer 130, and the second region is used to locate the first electrode 112.

In one embodiment, a buffer layer (not shown) can be sandwiched between the substrate 100 and the first semiconductor layer 110. Because the first semiconductor layer 110 and the substrate 100 have different lattice constants, the buffer layer is used to reduce the lattice mismatch, thus the dislocation density of the first semiconductor layer 110 will decrease. The thickness of the buffer layer ranges from about 10 nanometers to about 300 nanometers, and the material of the buffer layer can be GaN or AlN.

Referring to FIG. 1 and FIG. 2, the second surface of the first semiconductor layer 110 is a patterned surface. The first semiconductor layer 110 can be separated into a main body 110 a and a protruding part 110 b and distinguished by an “interface.” The interface can be parallel with the first surface of the first semiconductor layer 110. The interface is defined as a surface of the main body 110 a hereafter, and the protruding part 110 b extends away from the surface of the main body 110 a. The protruding part 110 b defines the plurality of three-dimensional nano-structures 113, and the plurality of three-dimensional nano-structures 113 form the patterned surface of the first semiconductor layer 110. The three-dimensional nano-structure 113 can be a protruding structure. The protruding structure protrudes out from the interface of the main body 110 a. The plurality of three-dimensional nano-structures 113 is a protruding structure located on the surface of the main body 110 a.

The plurality of three-dimensional nano-structures 113 can be arranged side by side. Each of the three-dimensional nano-structures 113 can extend along a straight line, a curvy line, or a polygonal line. The extending direction is substantially parallel with the surface of the first semiconductor layer 110. The two adjacent three-dimensional nano-structures are arranged a certain distance apart from each other. The distance ranges from about 0 nanometers to about 1000 nanometers, such as 10 nanometers, 30 nanometers, or 200 nanometers. The extending direction of the three-dimensional nano-structure 113 can be fixed or varied. While the extending direction of the three-dimensional nano-structure 113 is fixed, the plurality of three-dimensional nano-structures 113 extends along a straight line, otherwise the three-dimensional nano-structures 113 extends along a polygonal line or a curvy line. The cross-section of the three-dimensional nano-structure 113 along the extending direction is M-shaped. Referring to FIG. 3, the three-dimensional nano-structures 113 are a plurality of substantially parallel bar-shaped protruding structures extending along a straight line. The plurality of three-dimensional nano-structures 113 are substantially uniformly and equidistantly distributed on the entire surface of the main body 110 a.

Also referring to FIG. 4, the three-dimensional nano-structure 113 extends from one side of the semiconductor layer 110 to the opposite side along the X direction. The Y direction is substantially perpendicular to the X direction and substantially parallel with the surface of the main body 110 a. The three-dimensional nano-structure 113 is a double-peak structure including two peaks. The cross-section of the double-peak structure is in the shape of an M. The first peak 1132 and the second peak 1134 substantially extend along the X direction. The first peak 1132 includes a first surface 1132 a and a second surface 1132 b. The first surface 1132 a and the second surface 1132 b intersect to form an intersection line and an included angle θ of the first peak 1132. The intersection line can be a straight line, a curvy line, or a polygonal line. The included angle θ is greater than 0 degree and smaller than 180 degrees. In one embodiment, the included angle θ ranges from about 30 degrees to about 90 degrees. The first surface 1132 a and the second surface 1132 b can be planar, curvy, or wrinkly. In one embodiment, the first surface 1132 a and the second surface 1132 b are planar. The first surface 1132 a intersects the surface of the main body 110 a at an angle α. The angle α is greater than 0 degrees and less than or equal to 90 degrees. In one embodiment, the angle α is greater than 80 degrees and less than 90 degrees. The first surface 1132 a includes a side connected to the surface of the substrate 100, and extends away from the main body 110 a to intersect the second surface 1132 b. The second surface 1132 b includes a side connected with the second peak 1134 and extends away from the main body 110 a at an angle β. The angle β is greater than 0 degrees and smaller than 90 degrees.

The second peak 1134 includes a third surface 1134 a and a fourth surface 1134 b. The structure of the second peak 1134 is substantially the same as that of the first peak 1132. The third surface 1134 a and the fourth surface 1134 b intersect each other to form the included angle of the second peak 1134. The third surface 1134 a includes a side intersected with the surface of the main body 110 a, and extends away from the main body 110 a to intersect with the fourth surface 1134 b. The fourth surface 1134 b includes a side intersecting the third surface 1134 a to form the included angle of the second peak 1134, and extends to intersect the second surface 1132 b of the first peak 1132 to define a first groove 1136. A second groove 1138 is defined between two adjacent three-dimensional nano-structures 113. The second groove 1138 is defined by the third surface 1134 a of the second peak 1134 and the first surface 1132 a of the first peak 1132 of the adjacent three-dimensional nano-structure 113.

The first peak 1132 and the second peak 1134 protrude out of the main body 110 a. The height of the first peak 1132 and the second peak 1134 is arbitrary and can be selected according to need. In one embodiment, both the height of the first peak 1132 and that of the second peak 1134 range from about 150 nanometers to about 200 nanometers. The height of the first peak 1132 can be substantially equal to that of the second peak 1134. The highest points of the first peak 1132 and the second peak 1134 are defined as the farthest point away from the surface of the main body 110 a. In one three-dimensional nano-structure 113, the highest point of the first peak 1132 is spaced from that of the second peak 1134 a certain distance ranging from about 20 nanometers to about 100 nanometers. The first peak 1132 and the second peak 1134 extend substantially along the X direction. The cross-section of the first peak 1132 and the second peak 1134 can be trapezoidal or triangular, and the shape of the first peak 1132 and the second peak 1134 can be substantially the same. In one embodiment, the cross-sections of the first peak 1132 and the second peak 1134 are triangular. In one embodiment, the first peak 1132, the second peak 1134, and the main body 110 a form an integrated structure. Because of the limitation of the technology, the first surface 1132 a and the second surface 1132 b cannot be absolutely planar.

In each M-shaped three-dimensional nano-structure 113, the first peak 1132 and the second peak 1134 define the first groove 1136. The extending direction of the first groove 1136 is substantially the same as the extending direction of the first peak 1132 and the second peak 1134. The cross-section of the first groove 1136 is V-shaped. The depth h₁ of the first groove 1136 in different three-dimensional nano-structures 113 is substantially the same. The depth h₁ is defined as the distance between the highest point of the first peak 1132 and the lowest point of the first groove 1136. The depth of the first groove 1136 is less than the height of the first peak 1132 and the second peak 1134.

The second groove 1138 extends substantially along the extending direction of the three-dimensional nano-structures 113. The cross-section of the second groove 1138 is V-shaped or an inverse trapezium. Along the extending direction, the cross-section of the second groove 1138 is substantially the same. The depth h₂ of the second grooves 1138 between each two adjacent three-dimensional nano-structures 113 is substantially the same. The depth h₂ is defined as the distance between the highest point and the lowest point of the groove of the second groove 1138. The depth of the second groove 1138 is greater than the depth of the first groove 1136, and the ratio between h₁ and h₂ ranges from about 1:1.2 to about 1:3 (1:1.2≦h₁:h₂≦1:3). The depth of the first groove 1136 ranges from about 30 nanometers to about 120 nanometers, and the depth of the second groove 1138 ranges from about 90 nanometers to about 200 nanometers. In one embodiment, the depth of the first groove 1136 is about 80 nanometers, and the depth of the second groove 1138 is about 180 nanometers. The depth of the first groove 1136 and the second groove 1138 can be selected according to need.

The width of the three-dimensional nano-structure 113 ranges from about 100 nanometers to about 200 nanometers. The width of the three-dimensional nano-structure 113 is defined as the maximum span of the three-dimensional nano-structure 113 along the Y direction. The span of the three-dimensional nano-structure 113 gradually decreases along the direction away from the substrate 100. Thus in each three-dimensional nano-structure 113, the distance between the highest point of the first peak 1132 and the highest point of the second peak 1134 is less than the width of the three-dimensional nano-structure 113. The plurality of three-dimensional nano-structures 113 can be distributed in a certain interval from each other, and the intervals can be substantially the same. The interval forms the second groove 1138. The distance λ₀ between the two adjacent three-dimensional nano-structures 120 ranges from about 0 nanometers to about 200 nanometers. The distance between each two adjacent three-dimensional nano-structures 120 can be substantially the same. The distance λ₀ can be increased with the increase of the height of both the first peak 1132 and second peak 1134, and decreased with the decrease of the height of both the first peaks 1132 and second peaks 1134. In the Y direction, the distance λ₀ can be increased, decreased, or periodically varied. If the distance λ₀=0, the cross-section of the second groove 1138 is V-shaped. If the distance λ₀>0, the cross-section of the second groove 1138 is in the shape of an inverse trapezium.

Along the Y direction, the plurality of three-dimensional nano-structures 113 is distributed in a certain period P. One period P is defined as the width λ of the three-dimensional nano-structures 113 added with the distance λ₀. The period P of the plurality of three-dimensional nano-structures 113 can range from about 100 nanometers to about 500 nanometers. The period P, the width λ, and the distance λ₀ satisfy the following formula: P=λ+λ₀. The period P, the width λ, and the distance λ₀ is measured in nanometers. The period P can be a constant, and λ₀ or λ can be a dependent variable. Furthermore, one part of the three-dimensional nano-structures 113 can be aligned in a first period, and another part of the three-dimensional nano-structures 113 can be aligned in a second period. In one embodiment, the period P is about 200 nanometers, the width λ is about 190 nanometers, and the distance λ₀ is about 10 nanometers.

The active layer 120 is located on the first region of the second surface of the first semiconductor layer 110. In one embodiment, the active layer 120 covers the entire surface of the first region. The active layer 120 is engaged with the first semiconductor layer 110. In detail, the active layer 120 covers the plurality of three-dimensional nano-structures 113, and the surface of the active layer 120 which is connected with the first semiconductor layer 110 forms a patterned surface. The active layer 120 also includes a plurality of third grooves and third peaks, the grooves being engaged with the first peaks 1132 and second peaks 1134, the peaks being engaged with the first grooves 1136 and second grooves 1138. The active layer 120 is a photon excitation layer and can be one of a single layer quantum well film or multilayer quantum well films. The active layer 120 is made of GaInN, AlGaInN, GaSn, AlGaSn, GaInP, or GaInSn. In one embodiment, the active layer 120 has a thickness of about 0.3 μm and includes one layer of GaInN and another layer of GaN. The GaInN layer is stacked with the GaN layer.

Referring also to FIG. 5, the second semiconductor layer 130 is located on the active layer 120. The surface of the second semiconductor layer 130 away from the active layer 120 is configured as the light emitting surface of LED 10. In one embodiment, the second semiconductor layer 130 covers the entire surface of the active layer 120 away from the substrate 100. The thickness of the second semiconductor layer 130 ranges from about 0.1 μm to about 3 μm. The second semiconductor layer 130 can be an N-type semiconductor layer or a P-type semiconductor layer. Furthermore, the type of the second semiconductor layer 130 is different from the type of the first semiconductor layer 110. In one embodiment the second semiconductor layer 130 is a P-type gallium nitride doped with Mg. Furthermore, the light emitting surface of the LED 10 defines the plurality of three-dimensional nano-structures 133 to form a patterned surface. The structure of the three-dimensional nano-structures 133 is the same as the structure of the three-dimensional nano-structures 113. The three-dimensional nano-structure 133 is a protruding structure extending away from the second semiconductor layer 130. The plurality of three-dimensional nano-structures 133 can be arranged side by side. The extending direction of the three-dimensional nanostructures 133 can be fixed or varied. The cross-section of the three-dimensional nanostructure 133 along the extending direction is M-shaped. Each M-shaped three-dimensional nano-structure 133 includes a first peak 1332 and a second peak 1334 extending along the same direction. A first groove 1336 is defined between the first peak 1332 and the second peak 1334. A second groove 1338 is defined between the two adjacent three-dimensional nano-structures 133. The depth of the first groove 1336 is smaller than the depth of the second groove 1338.

The first electrode 112 is electrically connected with the first semiconductor layer 110 and spaced from the active layer 120. The first electrode 112 covers at least part of the surface of the second region. The first electrode 112 is a single layer structure or a multi-layer structure. The first electrode 112 can be an N-type electrode or a P-type electrode depending on the first semiconductor layer 110. The material of the first electrode 112 can be titanium (Ti), silver (Ag), aluminum (Al), nickel (Ni), gold (Au), or any combination of them. The material of the first electrode 112 can also be indium-tin oxide (ITO) or carbon nanotube film. In one embodiment, the first electrode 112 is a two-layer structure consisting of a Ti layer with a thickness of about 15 nm and an Au layer with a thickness of about 100 nm.

The second electrode 132 can be an N-type electrode or P-type electrode. In one embodiment, the second electrode 132 is located on the light emitting surface of LED 10. In detail, the second electrode 132 covers at least part of the three-dimensional nano-structures 133. The type of the second electrode 132 is the same as the second semiconductor layer 130. The shape of the second electrode 132 is arbitrary and can be selected according to need. The second electrode 132 covers a part of the surface or the entire surface of the second semiconductor layer 130. The material of the second electrode 132 can be Ti, Ag, Al, Ni, Au, or any combination of them.

Furthermore, a reflector layer (not shown) can be located on the surface of substrate 100 away from the active layer 120. The material of the reflector can be Ti, Ag, Al, Ni, Au, or any combination thereof. The reflector includes a smooth surface having a high reflectivity. The photons reach the reflector and will be reflected by the reflector, thus these photons can be extracted out of the LED 10 to improve the light extraction efficiency of the LED 10.

The first semiconductor layer 110 includes a plurality of three-dimensional nano-structures to form a patterned surface, and the active layer 120 is located on the patterned surface, thus the contact area between the first semiconductor layer 110 and the active layer 120 is enlarged. The electron-hole recombination density is improved, and the quantity of photons is increased. The light extraction efficiency of the LED 10 can be improved.

One embodiment of a method for making the LED 10 includes the following steps:

S11, providing a substrate 100 with an epitaxial growth surface 101;

S12, growing a first semiconductor layer 110 on the epitaxial growth surface 101;

S13, forming a plurality of three-dimensional nano-structures 113 on the first semiconductor layer 110;

S14, growing an active layer 120 and a second semiconductor layer 130 on the surface of the plurality of three-dimensional nano-structures 113 in that order;

S15, forming a plurality of three-dimensional nano-structures 133 by etching the surface of the second semiconductor layer 130 away from the active layer 120;

S16, applying a first electrode 112 electrically connected to the first semiconductor layer 110; and

S17, locating a second electrode 132 electrically connected to the second semiconductor layer 130.

Referring to FIG. 6, another embodiment of an LED 20 includes a substrate 100, a first semiconductor layer 110, an active layer 120, a second semiconductor layer 130, a first electrode 112, and a second electrode 132. The first semiconductor layer 110 includes a first surface and an opposite second surface. The first surface is in contact with the substrate 100. The active layer 120 and the second semiconductor layer 130 are stacked on the second surface and in that order. The surface of the second semiconductor layer 130 away from the active layer 120 is configured as the light emitting surface of the LED 10. The second surface of the first semiconductor layer defines a plurality of three-dimensional nano-structures 113. The surface of the active layer 120 away from the first semiconductor layer 110 defines a plurality of three-dimensional nano-structures 123. The light emitting surface of the LED 10 defines a plurality of three-dimensional nano-structures 133. The first electrode 112 is electrically connected with the first semiconductor layer 110, and the second electrode 132 is electrically connected with the second semiconductor layer 130. The plurality of three-dimensional nano-structures 123 is located on the surface of the active layer 120 away from the first semiconductor layer 110. The structure of the LED 20 is similar to that of the LED 10, except that a plurality of three-dimensional nano-structures 123 are located on the active layer 120 away form the first semiconductor layer 110.

Referring to FIG. 7, the plurality of three-dimensional nano-structures 123 forms a patterned surface on the active layer 120. The three-dimensional nano-structure 123 is similar to the three-dimensional nano-structures 113. Each three-dimensional nano-structure 123 includes a first peak 1232, a second peak 1234, a first groove 1236 defined between the first peak 1232 and the second peak 1234, and a second groove 1238 defined between two adjacent three-dimensional nano-structures 123. The distribution and alignment of the three-dimensional nano-structures 123 is the same as the distribution and alignment of the three-dimensional nano-structures 113. The second semiconductor layer 130 is located on the surface of the three-dimensional nano-structures 113, thus the surface of the second semiconductor layer 130 near the active layer 120 forms a patterned surface.

In the LED 20, the surface of the second semiconductor layer 130 in contact with the active layer 120 also includes a plurality of three-dimensional nano-structures 123, thus the contact area between the semiconductor layer and the active layer is also enlarged. The electron-hole recombination density is further increased, and the light extraction efficiency of the LED 20 can be improved.

One embodiment of a method for making the LED 20 includes the following steps:

S21, providing a substrate 100 having an epitaxial growth surface 101;

S22, growing a first semiconductor layer 110;

S23, forming a plurality of three-dimensional nano-structures 113 on a surface of the semiconductor layer 110;

S24, growing an active layer 120 on the surface of the three-dimensional nano-structures 113, and forming a plurality of three-dimensional nano-structures 123 on the surface which is away from the first semiconductor layer 110;

S25, growing a second semiconductor layer 130 on the surface of three-dimensional nano-structures 123;

S26, forming a plurality of three-dimensional nano-structures 133 on the surface of the semiconductor layer 130;

S27, applying a first electrode 112 on the surface of the first semiconductor layer 110; and

S28, applying a second electrode 132 electrically connected to the second semiconductor layer 130.

The method of making the LED 20 is similar to the method for making the LED 10, except that the LED 20 further forms the plurality of three-dimensional nano-structures 123 on the surface of the active layer 120 away from the first semiconductor layer 110. The substrate 100 with the first semiconductor layer 110 is located in a vertical epitaxial growth reactor, and the active layer 120 grows by a vertical epitaxial growth method. Thus the distribution and alignment of the three-dimensional nano-structure 123 can be the same as the distribution and alignment of the three-dimensional nano-structure 113.

Referring to FIG. 8, another embodiment of an LED 30 includes a substrate 100, a first semiconductor layer 110, an active layer 120, a second semiconductor layer 130, a first electrode 112, and a second electrode 132. The first semiconductor layer 110 includes a first surface and the second surface opposite to the first surface. The substrate 100 contacts the first surface of the first semiconductor layer 110. The active layer 120 and the second semiconductor layer 130 are stacked on the second surface of the first semiconductor layer 110, and in that order. The surface of the second semiconductor layer 120 away from the active layer 120 is configured as the light emitting surface of the LED 10. The second surface of the first semiconductor layer 110 defines a plurality of three-dimensional nano-structures 113. The surface of the substrate 100 contacting the first semiconductor layer 110 defines a plurality of three-dimensional nano-structures 103. The first electrode 112 is electrically connected with the first semiconductor layer 110, and the second electrode 132 is electrically connected with the second semiconductor layer 130. The structure of the LED 30 is similar to the structure of the LED 10, except that the LED 30 further includes the plurality of three-dimensional nano-structures 103 located on the surface of the substrate 100 which contacts the first semiconductor layer 110.

The plurality of three-dimensional nano-structures 103 forms a patterned surface. The three-dimensional nano-structure 103 is similar to the three-dimensional nano-structures 113. The distribution and alignment of the three-dimensional nano-structures 103 is the same as that of the three-dimensional nano-structures 113. The first semiconductor layer 110 is located on the surface of the three-dimensional nano-structures 103, thus the surface of the first semiconductor layer 110 near the substrate 100 forms a patterned surface.

One embodiment of a method for making the LED 30 includes the following steps:

S31, providing a substrate 100;

S32, forming a plurality of three-dimensional nano-structures 103 on a surface of the substrate 100 to form a patterned epitaxial growth surface 101;

S33, growing a first semiconductor layer 110 on the patterned epitaxial growth surface 101;

S34, forming a plurality of three-dimensional nano-structures 113 on a surface of the semiconductor layer 110;

S35, growing an active layer 120 and a second semiconductor layer 130 on the surface of three-dimensional nano-structures 113;

S36, applying a first electrode 112 on the surface of the first semiconductor layer 110; and

S37, applying a second electrode 132 electrically connected to the second semiconductor layer 130.

Photons reaching the plurality of three-dimensional nano-structures 103 with a large incident angle can be reflected, changing the direction of the moving photons so that the photons can be extracted from the light emitting surface. Furthermore, because the three-dimensional nano-structure 103 is M-shaped, the three-dimensional nano-structures 103 function as two layers of three-dimensional nano-structures assembled together, and the light extraction efficiency of the LED 30 will be improved.

Referring to FIG. 9, another embodiment of an LED 40 includes a substrate 100, a first semiconductor layer 110, an active layer 120, a second semiconductor layer 130, a first electrode 112, and a second electrode 132. The first semiconductor layer 110 includes a first surface and the second surface opposite to the first surface. The substrate 100 contacts the first surface of the first semiconductor layer 110. The active layer 120 and the second semiconductor layer 130 are stacked on the second surface of the first semiconductor layer 110 in that order. The surface of the second semiconductor layer 120 away from the active layer 120 is configured as the light emitting surface of the LED 10. The second surface of the first semiconductor layer 110 defines a plurality of three-dimensional nano-structures 113. The surface of the active layer 120 away from the first semiconductor layer 110 defines a plurality of three-dimensional nano-structures 123. The surface of the substrate 100 contacting the first semiconductor layer 110 defines a plurality of three-dimensional nano-structures 103. The first electrode 112 is electrically connected with the first semiconductor layer 110, and the second electrode 132 is electrically connected with the second semiconductor layer 130. The structure of the LED 40 is similar to the structure of the LED 30, except the LED 40 further includes the plurality of three-dimensional nano-structures 123 located on the surface of the active layer 120 away from the first semiconductor 110.

The three-dimensional nano-structure 123 is similar to the three-dimensional nano-structures 113. The distribution and alignment of the three-dimensional nano-structures 123 is the same as the distribution and alignment of the three-dimensional nano-structures 113.

Depending on the embodiment, certain of the steps of methods described may be removed, others may be added, and the sequence of steps may be altered. It is also to be understood that the description and the claims drawn to a method may include some indication in reference to certain steps. However, the indication used is only to be viewed for identification purposes and not as a suggestion as to an order for the steps.

It is to be understood that the above-described embodiments are intended to illustrate rather than limit the disclosure. Variations may be made to the embodiments without departing from the spirit of the disclosure as claimed. It is understood that any element of any one embodiment is considered to be disclosed to be incorporated with any other embodiment. The above-described embodiments illustrate the scope of the disclosure but do not restrict the scope of the disclosure. 

What is claimed is:
 1. A light emitting diode, comprising: a substrate; a first semiconductor layer having a first surface contacting the substrate and a second surface opposite to the first surface; an active layer stacked on the second surface of the first semiconductor layer; a second semiconductor layer stacked on the active layer and having a light emitting surface away from the active layer; a first electrode electrically connected with the first semiconductor layer; a second electrode electrically connected with the second semiconductor layer; and a plurality of three-dimensional nano-structures located on the second surface of the first semiconductor layer and on the light emitting surface, wherein each of the plurality of three-dimensional nano-structures has a first peak and a second peak aligned side by side, a first groove is defined between the first peak and the second peak, a second groove is defined between each two adjacent three-dimensional nano-structures of the plurality of three-dimensional nano-structures, and a depth of the first groove is less than a depth of the second groove.
 2. The light emitting diode of claim 1, wherein the each of the plurality of three-dimensional nano-structures is a bar-shaped protruding structure extending along a straight line, a curve line, or a polygonal line.
 3. The light emitting diode of claim 1, wherein a cross-section of the each of the plurality of three-dimensional nano-structures is M-shaped.
 4. The three-dimensional nano-structure array of claim 1, wherein the first peak comprises a first surface and a second surface intersecting each other to form a first include angle, the second peak comprises a third surface and a fourth surface intersecting each other to form a second include angle, and both the first include angle and the second include angle range from about 30 degrees to about 90 degrees.
 5. The light emitting diode of claim 4, wherein a cross-section of the first peak has a shape of a trapezoid or a triangle, and a cross-section of the second peak has a shape of a trapezoid or a triangle.
 6. The light emitting diode of claim 1, wherein a surface of the active layer is engaged with the plurality of three-dimensional nano-structures located on the first semiconductor layer.
 7. The light emitting diode of claim 1, wherein a depth of the first groove ranges from about 30 nanometers to about 120 nanometers, and a depth of the second groove ranges from about 100 nanometers to about 200 nanometers.
 8. The light emitting diode of claim 1, wherein the plurality of three-dimensional nano-structures is aligned side by side and extends to form a plurality of concentric circles or concentric rectangles.
 9. The light emitting diode of claim 1, wherein the plurality of the three-dimensional nano-structures is periodically aligned, and a period of the plurality of the three-dimensional nano-structures ranges from about 100 nanometers to about 500 nanometers.
 10. The light emitting diode of claim 1, wherein a distance between each two adjacent three-dimensional nano-structures of the plurality of three-dimensional nanostructures ranges from about 0 nanometers to about 200 nanometers.
 11. The light emitting diode of claim 1, wherein a width of the plurality of three-dimensional nano-structures ranges from about 100 nanometers to about 300 nanometers.
 12. The light emitting diode of claim 1, wherein a surface of the first semiconductor layer away from the substrate comprises a first region and a second region, the second semiconductor layer and the active layer are located on the first region, the second region is exposed from the second semiconductor layer and the active layer, and the first electrode is located on the second region.
 13. The light emitting diode of claim 1, further comprising a reflector located on a surface of the substrate away from the first semiconductor layer. 